Nitrite is oxidised to nitrate with the help of

Options

A. (a) Nitrosomonas
B. (b) Nitrococcus
C. (c) Nitrobacter
D. (d) Thiobacillus

Explanation

### Step-by-Step Solution:

1. **Understanding Nitrification**: Nitrification is a biological process in which ammonia (NH₃) is converted into nitrate (NO₃⁻) through an intermediate step involving nitrite (NO₂⁻). This process is essential for the nitrogen cycle in ecosystems.

2. **The Role of Bacteria**: Nitrification is carried out by specific types of bacteria known as nitrifying bacteria. These bacteria facilitate the oxidation of ammonia to nitrite and then nitrite to nitrate.

3. **Identifying the Bacteria**: The question specifically asks which bacteria oxidizes nitrite to nitrate. Among the options provided:
- **A. Nitrosomonas**: This bacterium primarily converts ammonia to nitrite.
- **B. Nitrococcus**: This bacterium is involved in the nitrification process but is less commonly referenced in the context of nitrite oxidation.
- **C. Nitrobacter**: This is the bacterium responsible for oxidizing nitrite to nitrate.
- **D. Thiobacillus**: This bacterium is involved in sulfur oxidation and is not directly related to the nitrification process.

4. **Conclusion**: Based on the roles of the bacteria listed, the correct answer to the question "Nitrite is oxidised to nitrate with the help of" is **C. Nitrobacter**.

5. **Final Statement**: Hence, nitrite is oxidized to nitrate with the help of Nitrobacter.